1. Field of the Invention
The present invention pertains to an apparatus and method for noninvasive stimulation of muscles in the upper airway to diagnose and/or treat a breathing disorder, such as obstructive sleep apnea In particular, the present invention pertains to a magnetic stimulation device and a method of using the device to apply pulsed magnetic fields to the muscles in the neck area of a patient to induce tension in such muscles, thereby relieving the obstructive sleep apnea caused by a relaxation of such muscles. By measuring an awake patient's compliance in the presence and absence of the magnetic stimulation, the likelihood that the patient suffers from obstructive sleep apnea can be determined.
2. Description of the Related Art
Obstructive sleep apnea (OSA) is a condition in which sleep is repeatedly interrupted by an inability to breathe due to an obstructed upper airway segment. Those afflicted with OSA experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently during sleep with potentially severe degrees of oxyhemoglobin desaturation. These symptoms may be translated clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of OSA include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Hypersomnolent sleep apnea patients may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Studies of the mechanism of collapse of the airway suggest that during some stages of sleep, there is a general relaxation of the muscles which stabilize the upper airway segment. This general relaxation of the muscles is believed to be a factor contributing to OSA.
Existing therapeutic remedies for treating OSA include the surgical removal of deformed, loose or swollen structures in the upper airway. It is also known to apply positive air pressure at the mouth and/or nose of the patient to “splint” the airway, thereby maintaining an open passage to the lungs. In addition, pharmacologic solutions have also been pursued.
Neither of these therapies is successful in all cases. Surgical relief is invasive, introduces a potential for surgical complications and is appropriate in only a small percentage of cases. On the other hand, the nasal mask needed to apply a positive air pressure is not tolerated by some OSA patients. Pharmacological therapy has been, in general, less than satisfactory, and side effects are frequent.
It is also known to treat OSA by electrically stimulating the musculature in the neck area associated with the upper airway. One such method of electrically stimulating the muscles in the upper airway area of a patient involves placing an electrode in direct contact with a surface of the patient and passing a current through the surface tissues of the patient contacting the electrode. For example, an intraoral appliance has been developed that applies electrical currents to the tongue, causing it to contract, thereby helping to clear the airway. Another known appliance applies electrical stimulation to the exterior surface of the patient's neck below the chin to induce contraction of the upper airway muscles.
Electrical stimulation using surface mounted electrodes creates relatively large current densities at the site of the electrodes. Because these current densities are disposed at the surface of the patient, which also contains a relatively large number of nerve endings, such electrical stimulation devices can cause unpleasant or painful sensations, possibly arousing the user from sleep.
It is also known to apply electrical stimulation to the muscles of the upper airway via electrodes implanted in the patient. Subcutaneous electrodes have the benefit of being positioned adjacent to the muscle or nerve to be stimulated to focus the electrical energy on that muscle/nerve while reducing the amount of collateral tissues effected by the high current densities near the electrode. There are also typically fewer nerve endings deep within the patient than at the surface. Thus, electrical stimulation using implanted electrodes reduces the likelihood that the electrical stimulation will induce an unpleasant or painful sensation in the patient. However, electrical muscle stimulation utilizing implanted electrodes requires surgical intervention, the permanent presence of foreign materials within the patient's neck tissue, and at least one electrical connection protruding from the patient. Consequently, there is a potential for infection or irritation at the surgical site and at the site where the electrode protrudes through the surface of the patient.